U.S. patent number 4,494,121 [Application Number 06/376,292] was granted by the patent office on 1985-01-15 for direction finding antenna.
This patent grant is currently assigned to Interstate Electronics Corporation. Invention is credited to Peter Bohley, Robert P. Couture, Carlton H. Walter.
United States Patent |
4,494,121 |
Walter , et al. |
January 15, 1985 |
**Please see images for:
( Certificate of Correction ) ** |
Direction finding antenna
Abstract
A direction finding antenna for use in missiles and the like may
include arrays of log periodic monopole antennas. The antennas may
be constructed of thin, metallic stub regions laminated to an
insulative support backing as a part of a wing of a missile. The
antennas are triangular in shape in order to provide improved
performance and to conform to the shape of wings on the missile.
The antennas perform an aerodynamic function as parts of the wings
as well as performing an electromagnetic function in the direction
finding system. The antennas are provided with parallel feed lines
which extend along the base of the triangular antenna, connecting
with antenna stubs on both sides of the support backing, and
connecting together at the forward end of the antenna. The antenna
stubs are generally rectangular metallic sheets arranged in order
of increasing length on the support backing. Electrically longer
antenna stubs may be provided with zig-zag convolutions for
improved performance at lower radio frequencies.
Inventors: |
Walter; Carlton H. (Columbus,
OH), Bohley; Peter (Columbus, OH), Couture; Robert P.
(Irvine, CA) |
Assignee: |
Interstate Electronics
Corporation (CA)
|
Family
ID: |
23484408 |
Appl.
No.: |
06/376,292 |
Filed: |
May 10, 1982 |
Current U.S.
Class: |
343/708;
343/792.5 |
Current CPC
Class: |
H01Q
1/286 (20130101); H01Q 11/105 (20130101); H01Q
1/44 (20130101) |
Current International
Class: |
H01Q
11/00 (20060101); H01Q 1/27 (20060101); H01Q
11/10 (20060101); H01Q 1/44 (20060101); H01Q
1/28 (20060101); G09F 009/30 () |
Field of
Search: |
;343/705,708,711,712,713,792.5,7MS |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Blum; Theodore M.
Attorney, Agent or Firm: Knobbe, Martens, Olson &
Bear
Claims
What is claimed:
1. A direction finding antenna system for use on an aerospace
vehicle, said antenna system comprising:
a plurality of log periodic monopole antennas, wherein each of said
antennas includes a plurality of antenna stubs arranged in a
substantially log periodic sequence, wherein said stubs are mounted
on an aerodynamic wing on the outside of said vehicle in order to
conserve space inside said missile, and wherein at least one of
said stubs undulates so as to produce lower resonant frequencies
for said stubs; and
a feedline for each of said antennas and connected to said stubs so
that adjacent ones of said stubs are electrically out of phase, so
that performance of said plurality of said antennas is
preferentially enhanced in a forward direction towards the nose of
said vehicle thus improving the ability of said missile to track a
target.
2. The antenna system of claim 1 wherein each of said antennas
comprises a dielectric, insulative substrate having metallic foil
layers on both sides thereof, wherein said foil layers form said
antenna stubs so that adjacent antenna stubs are on opposite sides
of said substrate.
3. The antenna system of claim 2 wherein the width of each of said
stubs varies in a log periodic fashion.
4. The antenna system of claim 2 or 3 wherein said feedline for
each one of said antennas comprises a coaxial cable extending from
the rear of said antenna so that the coaxial outer conductor makes
electrical contact with each of said stubs on one side of said
substrate and so that the center conductor of said cable makes
electrical contact with each of said stubs on the opposite side of
said substrate.
5. The antenna system of claim 1 wherein said feedline for each one
of said antennas comprises a meandering conductive strip extending
from the front of said antenna and making electrical contact with
each of said stubs, with the length of said strip between adjacent
of said stubs being sufficient to cause said adjacent stubs to be
of opposite electrical polarity.
6. An antenna for use with radio frequency electromagnetic
radiation, said antenna comprising:
a plurality of means for resonating in response to electromagnetic
radiation, wherein each of said means resonates at differing
radiation frequencies and wherein at least one of said resonating
means has undulations which provide lower resonant frequencies for
said stubs;
means for supporting said means for resonating in a side by side
relationship, so that said means for resonating are arranged in a
substantially log periodic sequence;
means for coupling electromagnetic frequencies to said antenna by
making electrical contact to each of said means for resonating so
that adjacent of said means for resonating are of opposite
electrical polarity, and so that said means for resonating are
connected as monopoles.
7. The antenna of claim 6 wherein said means for mounting secures
said means for resonating to an aerodynamic wing on the outside of
an aerospace vehicle.
8. The antenna of claims 6 or 7 wherein said means for supporting
comprises a dielectric substrate and wherein said means for
resonating comprise antenna stubs formed in metal foil on said
substrate.
9. The antenna of claim 8 wherein said antenna stubs are formed on
opposing sides of said dielectric substrate in a staggered
relationship so that adjacent of the stubs are on opposite sides of
said dielectric substrate.
10. The antenna of claim 9 wherein the width of each of said
antenna stubs formed in metal foil is arranged in a substantially
log periodic sequence.
11. The antenna of claim 10 wherein the width of each of said
antenna stubs formed in metal foil is arranged so that adjacent of
said stubs have boundaries which are directly opposite across said
dielectric substrate.
12. The antenna of claim 9 wherein said means for coupling
comprises a first coaxial cable extending along a first side of
said dielectric substrate so that the coaxial outer conductor of
said first cable makes electrical contact with the stubs of said
first side, and so that the central conductor of said first cable
makes electrical contact with the stubs on the second side of said
substrate opposite said first side.
13. The antenna of claim 12 wherein said means for coupling further
comprises a second coaxial cable extending along said second side
of said dielectric substrate so that the coaxial outer conductor of
said second cable makes electrical contact with the stubs of said
second side, and so that the central conductor of said second cable
makes electrical contact with the stubs on the first side of said
substrate.
14. The antenna of claim 9 wherein said means for coupling provides
a pair of oppositely phased connectors for coupling to signal
processing circuitry.
15. The antenna of claim 6 wherein said means for coupling provides
a pair of oppositely phased connectors for coupling to signal
processing electronics.
16. The antenna of claims 6 or 7 wherein said means for resonating
comprise antenna stubs and said means for coupling comprises a
meandering conductive strip extending between and making contact
with said antenna stubs, with the length of said strip between
adjacent of said stubs being sufficient to cause said adjacent
stubs to be of opposite electrical polarity.
17. The antenna of claim 16 wherein the length of each of said
antenna stubs is arranged in a substantially log periodic sequence.
Description
FIELD OF THE INVENTION
This invention relates generally to electromagnetic antennas and is
particularly concerned with direction finding antennas for use with
aerospace missiles.
BACKGROUND OF THE INVENTION
Direction finding systems using antennas or arrays of antennas have
been used in the past on self-propelled aerospace missiles in order
to provide steering information to the missiles. The direction
finding systems are a form of active or passive radar in which the
antennas are used to transmit and receive or receive only,
respectively, pulsed electromagnetic signals from the target. The
radar technique used may include amplitude or phase monopulse
systems. Missiles have been built which have antenna arrays or
miniature scanning antennas mounted in the nose of the missile.
Such designs are disadvantageous in that precious space inside the
missile is consumed by bulky antennas.
The construction and operation of logarithmically periodic antennas
is discussed in a two-part series of articles entitled "Log
Periodic Antennas", written by Al Brogdon, and which were published
on pages 81-85 of the October, 1967 issue of CQ Magazine and on
pages 80-85 of the November, 1967 issue of that magazine, the
disclosures of which are incorporated herein by reference.
The theory of frequency-independent log-periodic antennas is
discussed on pages 18-48 and 18-49 of a chapter entitled "Antennas
and Wave Propagation" by W. F. Croswell in Electronics Engineers'
Handbook, Donald G. Fink (ed.), (McGraw Hill: 1975). Prior art
tracking radar techniques are shown on pages 25-53 through 25-58 in
a chapter entitled "Radar, Navigation, and Underwater Sound
Systems" by David K. Barton in that same handbook. The two handbook
disclosures are incorporated herein by reference.
A variety of wide bandwidth, logarithmically periodic antennas have
been used in the past for radio wave reception by amateur ratio
operators and others. Logarithmically periodic dipole antennas have
been made which consist of a planar arrangement of parallel stubs
arranged in equal-length pairs mounted on opposing sides of a boom
with alternating feed connections between the stubs.
SUMMARY OF THE INVENTION
The direction finding antenna system of this invention has an array
of antennas for mounting on the outside circumference of a
generally cylindrical aerospace missile. Valuable space inside the
missile is conserved through this invention, thus allowing the
missile to be physically smaller (an advantage) or to contain
additional items in the space which would be occupied by the
direction finding antennas. The antennas of this invention have a
flat, triangular shape which may be attached to or used as
aerodynamic wings on the missile. Such a shape for the antennas is
advantageous in that the streamlined shape of the missile is not
disturbed by the antennas and the antennas may be securely attached
to or become aerodynamically functional wings on the missile.
The antenna elements of this invention are constructed as
spaced-apart thin metallic stub regions laminated to a dielectric,
insulating support backing substrate. It is preferable that the
antennas be fabricated using conventional double-sided printed
circuit board etching techniques so that the size and geometry of
each antenna element is precisely controlled. Such a construction
allows precise control over the antenna shape and size which is
important to assure improved electromagnetic performance.
The antenna stubs are spaced apart in a logarithmically increasing
fashion and similarly have widths which increase logarithmically
along the length of the antenna. The short, narrow stubs are
positioned at the forward end of the antenna and primarily
contribute to the high frequency performance of the antenna. The
wide, tall stubs are positioned at the rearward end of the antenna
and primarily contribute to the low frequency performance of the
antenna. Undulating zig-zag convolutions may be used for low
frequency stubs in order to increase the effective electrical
length of the stubs and in order to improve the low frequency
performance of the antenna. The convolutions allow an antenna
having improved low frequency performance to fit within the maximum
size limitations for wings imposed by the aerodynamic requirements
of the missile.
The antenna element feedline may include a pair of conductors
extending along the length of the antenna element, adjacent to the
missile surface on opposite sides of the support backing, with each
of the conductors connected to the antenna stubs. That is, one of
the conductors connects to each of the stubs on one side of the
backing, and the other conductor connects to each of the stubs on
the other side of the backing. In one embodiment, one of the
conductors is coaxial, having a center wire which is insulated from
the stubs except at the forward end of the antenna, where it is
connected to the other conductor. Such a feedline arrangement is
compact and fits closely to the shape of an aerodynamic wing.
An alternative embodiment of the antenna of this invention includes
a pair of coaxial conductors for passing signals to and receiving
signals from the antenna. The pair of conductors is attached to the
feed of the antenna so that the phase of the signals to the two
connectors of the coaxial conductors are opposite. Such an
arrangement of dual connectors would be used by the signal
processing electronics attached to the antenna so that the phase of
the antenna can be selected by using either one or the other of the
two connectors. Such use of two connectors of opposite phase is
very useful in the operation of the signal processing electronics
by simplifying and making possible the measurement of sum and
difference patterns for an array of wing antennas mounted on a
missile body.
An alternative feedline design includes a meandering or undulating
feed strip for mounting perpendicular to said stubs, and on the
outer surface of said missile. The stubs are connected to the feed
strip at locations where the feed strip passes under the backing
support. The undulations of the feed strip have electrical lengths
which increase logarithmically along the length of the antenna so
that a proper phase delay is provided between the adjacent
stubs.
The preferred embodiment has the antenna stubs arranged in a
staggered sequence along the length of each side of the antenna
element so that adjacent stubs are on opposite sides of the support
backing. The feedline design insures that the adjacent stubs (which
are on opposite sides of the substrate backing) have opposing
electromagnetic phase thus improving the directional and gain
performance of the antenna.
The antennas are mounted in an array which usually includes four
antennas spaced around the circumference of the missile. A signal
processing circuit using standard hybrids is used to connect the
antenna elements to the radio transmitter/receiver. Arrays of
antennas may be combined so that differing types of antenna
elements may be used together; such as smaller, nose mounted
antennas for the higher frequencies and larger, tail mounted
antennas for the lower frequencies. The shape and construction of
the antenna elements of this invention produces a high degree of
directionality in an antenna array, which is an advantage in
direction finding systems. The arrays constructed using the
antennas of this invention also exhibit a high level of
electromagnetic sensitivity which is advantageous in direction
finding systems.
The wing antennas of this invention may be used in various
applications such as unmanned vehicle systems, rockets, drones,
various aerodynamic platforms, and land-based vehicles.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a missile having three direction finding
antenna arrays mounted thereon.
FIG. 2 is a left side view of a missile wing antenna wherein the
antenna stubs are shown shaded for contrast.
FIG. 3 is a right side view of the missile wing antenna of FIG. 2
and wherein the antenna stubs are shown shaded for contrast.
FIG. 4 is a left side view of an alternative embodiment missile
wing antenna including stubs having undulations and wherein the
antenna stubs are shaded for contrast.
FIG. 5 is a right side view of the missile wing antenna of FIG. 4
wherein the antenna stubs are shown shaded for contrast.
FIG. 6 is a partially cut away rear elevational view of the wing
antenna of FIGS. 2 and 3 mounted on the missile body of FIG. 1.
FIG. 6A is an alternative embodiment of the antenna feed structure
shown in FIG. 6.
FIG. 7 is a partially cut away front elevational view of the wing
antenna of FIGS. 2 and 3 mounted on the missile body of FIG. 1.
FIG. 7A is an alternative embodiment of the antenna feed structure
shown in FIG. 7.
FIG. 8 is a diagram showing the angular and dimensional
relationships for use with the log periodic monopole antenna of
this invention.
FIG. 9 is a front perspective view of an alternative embodiment log
periodic monopole antenna using a meandering feedline.
FIG. 10 is a polar coordinate diagram on a logarithmic scale of the
propagation characteristics expected when an array of wing antennas
like those shown in FIGS. 2 and 3 is used on the missile body of
FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
Referring first to FIG. 1, the missile 10 is the usual type of self
propelled aerospace missile which may be dropped from an airplane
or otherwise launched and which is designed to use direction
finding radar to track a target or otherwise steer itself. The body
12 of the missile 10 is an elongated, circular metallic cylinder
which houses the missile rocket motor and electronics used in
guiding the missile. The body 12 has a nose or forward end 14
which, when the missile 10 is in flight, is kept pointed towards
the target. The missile body 12 has a rearward end or tail 16 which
encloses the missile rocket motor that propels the missile 10 in
flight.
When the missile 10 is in flight, it is kept on course towards a
target by a direction finding radar system which senses the
direction to the target by measuring the radio waves from the
target. The direction finding system is connected to control the
steering fins 18, 20, 22 and 24 (fin 24 is not shown) which serve
to steer the missile 10 so that the direction of flight of the
missile 10 is controlled.
Wing antennas 26, 28, 30 and 32 are (wing 32 is not shown) the four
wing antennas which are mounted just forward of the fins 18, 20,
22, and 24, respectively, on the missile body 12 and serve to
aerodynamically stabilize the missile 10 in flight, and also serve
as antennas for the direction finding radar system of the missile
10. The wings 26, 28, 30 and 32 generally have the shape of a right
triangle with the base of each triangularly shaped wing securely
attached to the missile body 12 and the hypotenuse of each triangle
sloping forwards towards the nose 14. Each of the wings 26, 28, 30
and 32 is relatively thin compared to its length and height and is
of streamline shape to readily pass through the air during the
flight of the missile 10. Each of the wing antennas 26, 28, 30, and
32 is provided with a plurality of antenna stub element regions on
the surface thereof so that each of the wing antennas forms a log
periodic monopole antenna. A plurality of forward wing antennas 34,
36, 38, and 40 (wing 40 is not shown) may be mounted forward
(towards nose 14) of the wings 26, 28, 30, 32, respectively. The
wings 34, 36, 38, and 40 are similar in construction to the wings
26, 28, 30 and 32, but are of smaller size. Tapered depth slot
antennas 42, 44, 46, and 48 (antenna 48 is not shown in FIG. 1) may
be mounted forward of the wings 34, 36, 38, and 40 for extended
high frequency coverage.
The rearward wing antennas 26, 28, 30, and 32 are parts of an
antenna array connected to the direction finding radar system in
order to provide response in a frequency sub-band of 100 megahertz
to 2000 megahertz. The forward wing antennas 34, 36, 38, and 40 are
elements in an antenna array connected to the direction finding
radar system of missile 10 in order to provide response in a
frequency sub-band of 2000 megahertz to 8000 megahertz. The tapered
depth slot antennas 42, 44, 46, and 48 are elements in an antenna
array connected to the direction finding radar system of missile 10
in order to provide response in the frequency sub-band from 8000
megahertz to 18 gigahertz.
Referring next to FIGS. 2 and 3, opposite (left and right) sides of
the same rearward wing antenna are shown in which the stub element
regions thereof are shown shaded. The stub element regions have a
height and width which determines their individual resonant
frequencies or optimum response frequencies. The wing antenna 50 is
shaped approximately like a right triangle and shows one of the
prototypes made during the testing of this invention. The wing
antenna 50 has a length of approximately 83 centimeters and a
height of approximately 21.5 centimeters and a thickness of
approximately 0.2 centimeters. The wing antenna 50 is a prototype
which was manufactured from standard, commercially available
printed circuit board material having a thin layer of electrically
conductive copper foil applied to both surfaces, and which was
etched by ferric chloride to form the pattern shown in FIGS. 2 and
3 wherein the shaded portions of FIGS. 2 and 3 indicate the copper
foil which was left after the ferric chloride etching process. The
wing antenna 50 is a prototype which was not intended for use as an
actual aerospace wing for mounting on the missile 10, but which was
built in order to test the performance of the configuration of the
antenna. It is anticipated that the same type of construction shown
in FIGS. 2 and 3 may be applied to the outward surfaces of
conventional aerodynamic missile wings, or otherwise incorporated
into conventional aerodynamic missile wings. For example, the sides
shown in FIGS. 2 and 3 may be separately fabricated and applied to
opposing surfaces of a missile wing, so that the missile wing is
sandwiched between the stubs of the two antenna sides. An
alternative approach would be to use the antenna itself as the core
of a built-up wing in which insulating structural reinforcing
materials may be attached to both sides of the antenna itself to
form an aerodynamic wing.
As shown in FIGS. 2 and 3, the etched copper foil pattern on each
side of the wing antenna 50 includes a plurality of antenna stubs
arranged in a spaced apart sequence wherein the spaces between
adjacent stubs decrease in a logarithmically periodic fashion along
the length of the wing antenna 50. The width of each of the stubs
is also arranged in a periodic, logarithmically decreasing sequence
(from back to front of wing 50) so that as the separation between
adjacent stubs decrease, the width of the stubs also decreases. The
width of each of the stubs shown in FIGS. 2 and 3 is given in the
following table in centimeters:
______________________________________ Stub No. Width
______________________________________ 52 2.0 centimeters 54 3.2 56
1.2 58 1.3 60 1.6 62 1.7 64 1.9 66 2.2 68 2.6 70 2.8 72 3.1 74 3.6
76 4.0 78 4.5 80 5.1 82 5.6 84 6.5 86 7.0 88 7.6
______________________________________
The stub 88 has a flat top which gives it a constant height of 21.5
centimeters. The stubs 52-86 are bounded above by a sloping
hypotenuse line which slopes downward from the height of 21.5
centimeters to intersect with the base of the triangular wing 50 in
a distance of 61 centimeters. All of the measurements given in this
description are approximate and are presented for the purposes of
illustration of possible embodiments of this invention. As can be
seen from FIG. 2, adjacent stub elements (such as 84, 86, and 88)
do not overlap; that is, the space between stubs 84 and 88 is as
large as the width of the stub 86 and the stub 86 is positioned
between the stubs 84 and 88, but on the opposite side of the wing
antenna 50.
Referring next to FIGS. 4 and 5, an alternative embodiment for the
wing antenna shown in FIGS. 2 and 3 is presented. FIGS. 4 and 5
show opposite sides of the same wing antenna 100. The wing antenna
100 is approximately 129.5 centimeters in length and 20 centimeters
in height. The width of each of the stub elements of the wing
antenna 100 is given in the following table:
______________________________________ Stub No. Width
______________________________________ 102 1.0 centimeters 104 2.1
106 1.2 108 1.4 110 1.4 112 1.6 114 1.7 116 1.9 118 2.1 120 2.2 122
2.3 124 2.5 126 2.9 128 3.1 130 3.4 132 3.6 134 3.9 136 4.2 138 5.1
140 4.9 142 5.5 144 6.2 146 6.1 148 7.2 150 7.3 152 8.6 154 9.1 156
10.0 158 10.1 ______________________________________
The wing antenna 100 shown in FIGS. 4 and 5 is very similar in
construction to the wing antenna 50 of FIGS. 2 and 3, and a major
difference is the type of stub construction particularly shown by
the stubs 152, 154, 156, and 158 of FIGS. 4 and 5. The stubs 152,
154, 156, and 158 use an undulating (zig-zag) back and forth folded
pattern which effectively increases the electrical length of the
stubs 152, 154, 156 and 158. The effect of using such undulations
or convolutions in the stubs 152, 154, 156 and 158 is to shift the
optimum performance frequency for those stubs to lower frequencies
than would otherwise be the case without such undulations. That is,
for example, if the stub 158 were to have a simple, 4-sided shape,
extending from the base to the hypotenuse of the wing 100, the stub
158 would have a higher optimal frequency of operation than with
the undulations shown in FIG. 4. The purpose of providing such
undulations in the stubs of the wing antenna 100 is to improve the
low frequency performance of the wing antenna 100 without requiring
an increase in the physical size of the wing antenna 100. An
important limitation on the physical size of the wing antenna 100
is the aerodynamic requirements imposed by the size and shape of
the missile 10.
Referring next to FIG. 6, the wing antenna 50 includes a triangular
dielectric backing substrate 200 which is preferably 0.090 inch
thick fiberglass printed circuit board material. The substrate 200
has layers of copper foil 202 and 204 on opposite surfaces thereof.
The copper foil 202 has the stub region pattern shown in FIG. 2,
and the copper foil 204 has the stub region pattern shown in FIG.
3.
The structures shown in FIGS. 6 and 7 may be used with the wing
antenna designs shown in FIGS. 2 and 3 or FIGS. 4 and 5. The feed
structures shown in FIGS. 6 and 7 perform the same function for the
respective parts of the two versions of the wing antenna (with one
version shown in FIGS. 2 and 3 and another version shown in FIGS. 4
and 5).
The prototype shown in FIGS. 6 and 7 is constructed using
commercially available printed circuit board material which is
provided with a substrate 200 and the layers 202 and 204. The
substrate 200 is securely attached to a dielectric supporting pad
206 which is preferably composed of fiberglass printed circuit
board material. The purpose of the support pad 206 is to provide
isolation between the wing antenna 50 and the missile body 12 and
also to provide firm mechanical connection between the wing antenna
50 and the missile body 12. As shown, the coaxial outer conductors
of the coaxial cables 90 and 92 are electrically connected to the
foil layers 202 and 204, respectively, and extend along the
channels formed by the intersection of substrate 200 with the
supporting member 206. As shown in FIG. 6 (the rearward end of wing
antenna 50), the coaxial cable 92 is provided with a cable
connector 94 for connection to the direction finding circuitry and
hybrids mounted inside the missile body 12. As shown in FIG. 7, the
center conductor 208 of the coaxial cable 92 extends through the
dielectric insulating substrate 200 at the forward end of the wing
antenna 50 and makes contact with the foil layer 202 at the forward
end of the wing antenna 50. The foil layer 204 is etched away at
the forward end of the wing antenna 50 so that the center conductor
208 of the coaxial cable 92 does not make contact with the foil
layer 204 at the forward end of the wing antenna 50.
The coaxial cables 90 and 92 shown in FIG. 6 form a feedline
structure for the wing antenna 50 which causes the stubs of foil
layer 204 to be of opposite electrical polarity or out of phase
with the stubs of foil layer 202. This difference in phase is
produced by connecting the coaxial outer conductor of cable 92 to
the foil layer 204, and by connecting the center conductor 208 of
the coaxial cable 92 to the foil layer 202. The feedline structure
forms a broadband balun for matching the coaxial line (at connector
94) to the parallel stubs. The center conductor of coaxial cable 92
is labeled 208. The feedline structure of FIGS. 6 and 7 performs an
important function in causing the electrical polarity of the stubs
of layer 202 to be opposite from the polarity of the stubs of layer
204. The difference in polarity is important in causing the wing
antenna 50 to function as a log-periodic monopole antenna.
Referring back to FIGS. 2 and 3, the connections of coaxial lines
90 and 92 shown in FIGS. 6 and 7 serves to ensure that the
electrical polarity of stubs 54, 58, 62, 66, 70, 74, 78, 82 and 86
are opposite to the polarity of stubs 52, 56, 60, 64, 68, 72, 76,
80, 84, and 88. For example, this ensures that the polarity of stub
82 (which is physically adjacent to stub 80) is of opposite
electrical polarity to that of stub 80. Such an out-of-phase
relationship is important in improving the effectiveness of the
wing antenna 50 by increasing the efficiency of the wing antenna 50
in both receiving and transmitting energy, and by improving the
directional characteristics (increasing the front to back ratio) of
the wing antenna 50 so that electromagnetic energy is
preferentially radiated towards and received from the forward end
of the wing antenna 50.
In the prototype constructed, the coaxial cables 90 and 92
consisted of flexible, commercially available coaxial wiring cable
mounted inside malleable, semi-rigid copper tubing which was
soldered to the foil layers 202 and 204, respectively. The braided
outer shield of the wiring cable is electrically connected to the
respective copper tubing for each of the cables 90 and 92.
The use of a wing insulating dielectric layer 200 allows the
adjacent antenna stubs to be very close together, and yet to be of
opposite polarity. The staggered arrangement of antenna stubs
provided by placing adjacent stubs on opposite sides of the
dielectric substrate 200 allows for a compact construction which is
compatible with the physical demands of aerodynamic missile wings;
i.e., the aerodynamic antenna carrying wing may be of small
thickness and generally have an elongated, right triangular
shape.
Referring next to FIGS. 6A and 7A, feed structures similar to those
shown in FIGS. 6 and 7 are used in an alternative embodiment which
provides a pair of connectors 94 and 302 which are of opposite
phase. The opposite electrical phase presented by connectors 300
and 302 is a result of the arrangement of the feed structures shown
in FIGS. 6A and 7A and is useful in the signal processing
electronics (not shown) in measuring the sum and difference
patterns for arrays of antennas as shown in FIG. 1.
The coaxial cables 90 and 92 shown in FIGS. 6A and 7A are similar
to those shown in FIGS. 6 and 7, excepting that (as shown in FIG.
6A), the cable 90 is equipped with a connector 302, and (as shown
in FIG. 7A) the center conductor 304 of cable 90 extends through
the substrate 200 and contacts the foil layer 204. Thus, the
arrangement and construction of the antenna feed structure formed
by coaxial cables 90 and 92 is symmetric about the substrate
200.
In practice, the selection is made in connecting to either
connector 94 or 302 in order to select the phasing of the antenna.
The phasing of the antenna is of particular importance when more
than one antenna are used in an array, so that the relative phase
relationship between the antennas in the array determines the
radiating properties of the array, and also determines the nature
of the sum and difference signals between antennas in the array. It
may be possible to provide electrical switching between connectors
94 and 302 so that the signal processing electronics (not shown)
may automatically select the appropriate phasing of the
antenna.
Referring next to FIG. 8, the following formulas may be used in
constructing the antennas of this invention:
.alpha.=angle of slope of the antenna
.tau.=ratio of heights or widths of adjacent stubs
.sigma.=ratio between the distance to the next adjacent shorter
stub and four times the height of the stub
H=height of a stub
D=distance between adjacent stubs ##EQU1##
For preferred performance:
The diagram of FIG. 8 shows a representation of the general type of
log periodic monopole antenna layout shown in FIGS. 2, 3, 4, and 5.
The formulas shown above may be used to determine the preferred
width of stubs to use, and the preferred separation between stubs.
The formulas above also detail the preferred ranges for the
variables (.tau. and .alpha.) used in the construction of the wing
antenna.
The number of stubs which should be included is limited by the
desired high frequency performance and the physical size
limitations at the forward end of the wing antenna. As shown in
FIGS. 4 and 5, convolutions may be added to the longer stubs in
order to lower their optimal performance frequency so that the wing
antenna has improved low frequency performance.
Referring next to FIG. 9, an antenna 258 having an alternative
construction for the feedline arrangement shown in FIGS. 6 and 7 is
presented. In FIG. 9, a meander feedstrip 250 interconnects antenna
stubs 252, 254, 256, 258, 260, 262, 264 and 266. The stubs 252-266
are arranged in a straight line by sequentially increasing height,
with the height of each stub and the distance between stubs
determined in accordance with the formulas presented above in
connection with FIG. 8. Although not shown in the figure, the
diameter of each stub may similarly be increased along the length
of the antenna in order to improve performance. A sufficient length
of meander feedstrip 250 is placed between adjacent stubs so that
the electrical phase delay between adjacent stubs is preferably
200.degree. to 225.degree. (the length of which depends on the
resonant frequencies of the stubs). The feedstrip 250 contacts the
lower portion of each of the antenna stubs 252-266 and undulates in
a back and forth pattern with the undulations (the length of each
of which is determined by the desired electrical phase shift)
increasing in size in moving from the front to the rear of the
antenna 258. The undulations increase in size along the length of
the antenna 258 because the optimal response frequencies of the
stubs at the rear of antenna 258 is lower than for those at the
front of antenna 258. The feedline 250 is terminated at the front
of the antenna 258 in a connector 256 for connection to the
direction finding electronics inside the missile 10. The stubs
252-266 may be circular cylinders of uniform diameter which may be
incorporated into an aerodynamic wing and mounted on a missile 10
(similarly to the mounting of wings 26, 28 and 30 in FIG. 1). In
practice, the feedstrip 250 is mounted over a dielectric insulator
(not shown) on the periphery of the missile body 12, which acts as
a ground plane.
The connector 268 is a coaxial connector in which the center
conductor of the connector 268 makes electrical contact with the
feedline 250, and in which the coaxial outer conductor of the
connector 268 is electrically connected to the ground plane (i.e.,
the periphery of the missile body 12). A portion of coaxial cable
251 extends between the connector 268 and the feedstrip 250 so that
the coaxial outer conductor of the cable 251 makes contact with the
periphery of the missile body 12, and so that the center conductor
of the cable 251 contacts the feedstrip 250.
Referring next to FIG. 10, a polar coordinate graph is shown of
relative (on a logarithmic scale) radiated electromagnetic power at
a frequency of 1000 megahertz in the azimuth plane for the type of
antenna shown in FIGS. 2 and 3; wherein four such antennas were
mounted about a mock-up of the missile body 12 as shown in FIG. 1.
A mock-up of the missile 10 was placed at the position indicated by
the intersection of the axes in FIG. 10, and was pointed towards
the point marked 0.degree.. The line represented by short dashes
and labeled "DIPOLE" corresponds to the reference radiation pattern
of a standard dipole antenna. The line represented by a solid line
and labeled "SIGMA (.SIGMA.)" corresponds to the summation of
antennas on both sides of the missile body 12. The line represented
by long dashes and labeled "DELTA (.DELTA.)" corresponds to the
difference between antennas on opposite sides of the missile body
12. This type of sum and difference information may be used by a
digital computer (not shown) of the direction finding electronics
inside missile 10 in order to properly guide the missile 10. FIG.
10 illustrates the high efficiency and directional sensitivity of
the antennas of this invention. The large response shown in the
forward half plane (270.degree. to 0.degree. to 90.degree.) versus
the small response shown in the backward half plane (90.degree. to
270.degree.) shows the large front-to-back ratio of the antenna of
this invention.
* * * * *